1. Field of the Invention
The present invention relates generally to surgical methods and medical devices. More particularly, it concerns methods and apparatuses useful in navigating the subarachnoid space, including the spinal and the intracranial subarachnoid spaces. It also concerns medical devices, such as sheaths, that are suited for attachment to the skin.
2. Description of Related Art
During the 20th century, brain neurosurgery has advanced via the introduction of microsurgical techniques, the development of new tools such as aneurysm clips, and the description of new operative approaches. Surgeons have developed elegant mechanisms to remove parts of the bones making up the skull (craniotomy) and operate on structures deep within the brain while attempting to minimize complications relating to the approach. [See, for example, Fries et. al., 1996.] Furthermore, the surgical approach to the intracranial and spinal subarachnoid space has historically consisted of the skin incision, dissection to either the cranium or spinal bony covering, removal of some bone, and dissection through the meninges to gain access to the neurological structures. While imaging modalities became integrated into diagnostic evaluations, only at the end of the last century were significant attempts made to integrate computed tomography, angiography, and most recently magnetic resonance (MR) scanning into the actual surgical procedures.
Unfortunately, craniotomy has limited the applicability of such imaging modalities because the surgeon cannot simultaneously stand at the patient's head and conveniently operate on the brain via craniotomy, maintain sterility, and scan the brain using a large scanning apparatus that requires the patient to be held within it. There are theoretical limits to the ability to conveniently perform such surgery using currently-available imaging devices due to a conflict between the means of acquiring images and the means of operating on the brain. Furthermore, in conventional neurosurgery, while the brain surface is readily available underlying a craniotomy, the approach to deeper structures is progressively more invasive in terms of retraction injury (i.e., the brain is often retracted after the craniotomy to facilitate access to different areas in and around the brain) or even the need to remove brain tissue to gain access.
During the last 20 years, the development of endovascular neurosurgery has resulted in the creation of specialized devices for application within arteries. These devices include not only catheters and guidewires, but also embolic materials that can be introduced via catheters, thereby enabling the enhancement of some procedures that are performed via craniotomy following embolization, and thereby eliminating the need for craniotomy altogether in other cases. However, these techniques have heretofore been limited to the intravascular space (i.e., the space within blood vessels) because that was seen as the only available route of access for catheterization of the intracranial contents.
Extravascular access to locations within the head for the purpose of facilitating the kinds of procedures heretofore performed following a craniotomy has not been reported to the inventor's knowledge. The subarachnoid space, which is a compartment that contains the body of the spinal cord and cerebrospinal fluid (CSF)—a fluid that fills and surrounds the ventricles (cavities) of the brain and the spinal cord, and acts as a lubricant and a mechanical barrier against shock—is one such extravascular route.
Some authors have described experimental data using endoscopy in the subarachnoid space. An endoscope is a tube with a light and a lens on the end that can be used to view various regions within a body. One group from Sweden utilized a relatively large (4 millimeter) bronchoscope (a type of endoscope) to travel the length of the subarachnoid space to eventually visualize the contents of the posterior fossa, as well as gain access to the ventricular system. [Stefanov et. al., 1996.] These studies were performed in cadavers and involved dissection to the lumbar space and introduction of the bronchoscope from that location, using only endoscopic guidance. Applications in the clinical setting were not advocated.
A group from Japan utilized a smaller endoscope in cadavers to access only the subarachnoid space around the spinal cord and posterior fossa. [Eguchi et. al., 1999.] No attempt was made to access either the ventricles or the supratentorial cisterns. The endoscopes used also had no directional capability. Uchiyama et. al. (1998) used a “myeloscope” (a type of endoscope) that was sufficiently small (0.5-2 mm) to safely access the spinal subarachnoid space without injuring the spinal cord in a group of patients. Neither of these articles discusses catheterizing the subarachnoid space, whether for the purpose of facilitating intracranial access or otherwise. Furthermore, neither group attempted navigation of the subarachnoid space using catheters and guidewires or other means to more precisely control device placement or other instrument insertion.
Amar et. al. (2001) recently described a technique of catheterizing the spinal epidural space for the introduction of medication. However, that technique did not involve catheterization of the subarachnoid space, nor was it performed for the purpose of facilitating intracranial access. Other techniques of delivering anesthetics and other therapeutic agents to the subarachnoid space using catheters are described in U.S. Pat. Nos. 5,085,631 and 5,470,318.
The techniques disclosed in these patents do not involve advancing the catheter toward the head of the patient after the catheter is introduced into the subarachnoid space. Nor do they involve steps that facilitate intracranial access. Neither patent discloses using catheters for introducing other medical devices through the passageways in those catheters for the purpose of facilitating intracranial access.
The inventor is aware of other techniques for delivering medicaments to the subarachnoid space using a catheter. However, of these, none involved the use of catheters for the purpose of facilitating intracranial access. [See, for example, Delhaas, 1996.]
In addition, medical devices (e.g., sheaths) that are used with the foregoing techniques to facilitate the introduction of endoscopes and catheters into the subarachnoid space are not well-suited for use with imaging modalities such as MR scanning. Generally, once a sheath is in place within a patient, other devices such as endoscopes and catheters can be introduced into the patient through the passageway within the sheath. In other words, once the sheath is in place, one end of the sheath is located beneath the patient's skin while the other end sticks out of the patient's skin, thereby allowing the surgeon to introduce, for example, an endoscope or catheter into the patient through the sheath's passageway. The manipulations that cause these introductions to occur are carried out at the end of the sheath that is positioned outside of the patient. However, a traditional sheath is sized and configured such that it does not extend very far outside of a patient once it has been inserted into a desired location. As a result, the manipulations of other medical devices introduced through the sheath cannot feasibly take place while the patient is positioned within an MR scanner (which mainly consists of large magnets) because there simply is not enough of the sheath sticking out of the patient to work with. Furthermore, this same shortcoming would impede a surgeon's ability to use one or more robotic devices to assist in or completely perform these manipulations.
Based on the foregoing, new methods of facilitating intracranial access that do not involve the shortcomings of craniotomy, and that can be monitored or guided via various imaging modalities are needed. New methods of facilitating intracranial access via devices introduced through non-endoscopic devices are also needed. Furthermore, new medical devices useful for establishing access to areas such as the subarachnoid space, and that can be used with robotic instruments or while the patient is positioned within an MR scanner are needed.